Prof. Dr. Jan Lohmann

Work in the department of Stem Cell Biology is focused on the regulatory programs governing shoot meristem function and the control of stem cell number in the reference plant Arabidopsis thaliana. To this end we employ an integrated approach of advanced genetic, genomic, and molecular methods together with computational analysis to determine how hard-wired genetic circuits underlying stem cell control are orchestrated and integrated with environmental signals.

Regulatory networks of stem cell control in the reference plant Arabidopsis

Few scientific topics currently attract as much attention as stem cells. While public debate has focused on embryonic stem cells from animals and humans, stem cells are common to all multicellular organisms. In most animals, the only “true” totipotent stem cell is the fertilised egg and its immediate descendants. Many plant cells, in contrast, continue to be totipotent throughout the plant’s life, and plant stem cells are much more easily obtained and analyzed than those of animals.

Plant stem cells reside at the growing points of a plant, namely the root tip and the shoot apex and are embedded into specialised structures called meristems, which provide a local environment that regulates the homeostasis between proliferation and differentiation. After the transition from vegetative to reproductive development of the plant, floral meristems arise from the main shoot apical meristem and then develop into flowers. Stem cell regulation and floral patterning in Arabidopsis are closely linked, since the homeodomain protein WUSCHEL (WUS) regulates stem cell fate in both shoot and floral meristems. In addition, WUS interacts with the flower-specific transcription factor LEAFY (LFY) to activate transcription of the floral homeotic gene AGAMOUS (AG), which is essential for the correct patterning of flowers. WUS and AG in turn form a negative feedback loop in which AGr epresses WUS to terminate the maintenance of stem cells in flowers, bringing about the determinate character of flowers.

Current research

1. How is stem cell fate initiated and maintained in the shoot apical meristem?

2. How are local transcriptional signals integrated with system wide hormonal signals to synchronize stem cell behaviour with the growth status of the entire plant?

3. How are environmental signals sensed and relayed to modulate shoot meristem activity?

Since the activity of the shoot meristem is controlled by a large number of factors, which cannot be studied in detail by a single group, we focus our analyses on four essential components of the regulatory network. First, we study the activity of the homeodomain transcription factor WUSCHEL (WUS) on a mechanistic basis, since WUS is essential for stem cell induction and maintenance. These experiments include the cell type specific identification of direct and indirect target genes, as well as the functional characterization of these factors. Second, we record the epigenetic states of various cell types of the meristem, including stem cells to gain a detailed understanding of their molecular identities. Third, we examine the interaction of cytokinin and auxin plant hormone signaling pathways with the core meristem regulation machinery provided by WUS. Special focus lies on the functional and regulatory analysis of A-type ARR genes. And fourth, we study the role of of environmental signals, such as daylenght and temperature, in modulating the activity of stem cells of the shoot apical meristem and investigate how mechanisms of short-trem acclimatization converge with long-term adaptation using natural genetic variation. Some selecetd publications are listed below.

He also is the spokesperson of the collaboartive research centre SFB873 "Maintenance and Differentiation of stem cells in Development and Disease", a member of the SFB1101, the CellNetworks Cluster of Excellence and the HBIGS graduate school.

Our work is supported by funds from a variety of public sources, including the DFG and the ERC.